Human invariant NKT cells are novel, distinct lymphocyte populations with a restricted T-cell receptor repertoire (Vα24-Vβ11). They play a pivotal role in immunoregulation and in anti-tumor activities. We focused on Vα24+NKT cells in colorectal carcinomas (CRC) and their clinicopathological significance. A total of 103 CRC cases were studied on Vα24+NKT cell infiltration immnohistochemically. The degree of NKT-cell infiltration in tumors was evaluated as low (<7 NKT cells/5 HPF) or high (【greater than or equal】7 NKT cells/5 HPF). The correlation between the degree of infiltrated Vα24+NKT cells and clinicopathological parameters was studied statistically. A small number of Vα24+NKT cells were found in the normal colorectal mucosa (2.6±3.7 cells/5HPF) ; however, their number increased remarkably in CRC (15.2±16.3/5HPF, P=0.0003). Higher NKT-cell infiltration was more frequent in women than in men (P=0.034) and correlated with fewer lymph node metastases (P=0.042). Patients with high NKT-cell infiltration showed higher overall (P=0.018) as well as disease-free (P=0.0006) survival rates. Intratumor NKT-cell infiltration was an independent prognostic factor for the overall (P=0.033) and disease-free (P=0.0064) survival rates. Increased infiltration of Vα24+NKT cells was observed in CRC. Higher Vα24+NKT cell infiltration in CRC was an independent prognostic factor for favorable prognosis. These results are important to create a new strategy against locally recurrent rectal cancer.